1. Field of the Invention
This invention relates to the field of automatic solid fuel stokers, and especially to a detachable overfeed fuel stoker adapted for substantially-unattended home use. The invention is particularly effective with soft, coking coal.
2. Prior Art
A number of devices are known in the art in which a rotational element such as a motor is connected by means of a linkage to a reciprocating element, in order to introduce fuel into a furnace. These devices are not adapted to wind up and release a spring or to suddenly unload stored energy, to thereby throw fuel onto the surface of a fire. Instead, prior art devices slowly and continuously feed quantities of coal, toward or under the fire. Although such a mechanism is effective and useful in connection with feeding of anthracite coal (i.e. hard coal), substantial difficulties are encountered when slow motion techniques are attempted using soft coal (bituminous or coking coal). With the soft coal, heat causes softening together with release of more-or-less volatile hydrocarbons. When heated, the chunks of coal become sticky and adhere to one another in a viscous mass.
Problems with simple adherence of coal chunks could presumably be overcome by employing a sufficiently deep bed of unburned coal that the coal could be added at a relatively-cool lowermost zone where it would not adhere, and thereafter moved vertically upwards as more coal was placed below. Unfortunately, with coking coal, the upper viscous heated layer tends to choke off the flow of oxygen. Therefore, underfeed devices are not particularly useful with soft coal. There are also difficulties in small scale installations such as home furnaces in that it is impractical or dangerous to have a quantity of unburned coal under the fire. Furthermore, continuous feeding from underneath precludes the possibility of ash removal from below the area of combustion, as is preferred in connection with home furnace installations.
Automatic stokers for the addition of coal to a fire, in which a piston is employed to periodically move an incremental quantity of coal from a bin to a combustion area are shown, for example, in U.S. Pat. Nos. 913,771--Roe, 1,177,430--Metesser, 1,605,665--Riler et al, 1,694,290--St. Clair, 1,736,565--Woodcock, 1,938,681--Beers and 2,276,659--Ciersinger. These devices, although effective at unloading bins, are each prone to certain difficulties if applied to home installations or if used with coking coal. Accordingly, they are normally used only with anthracite. Pusher means in the form of spaced fuel pusher bodies are provided along a rigid connection member with a reciprocating driving means, e.g., a piston. The pusher bodies, for example, have a flat front face, for pushing the coal on the forward stroke of the connection member, and an inclined rear face, to slide past the coal on the return stroke. In some installations, such pushers take the form of a reciprocating terraced fuel support, the advance of which carries fuel from the bin to the combustion area. In other devices, the pusher is a separate element either connected to the same linkage as the piston or periodically operable in some other manner. The point of these devices is to achieve a horizontal motion of the coal, towards the side and/or bottom of a pile of burning coal.
Inasmuch as prior art stoking devices are primarily intended for relatively large scale installations, it is the exception to find a stoker mechanism which is easily removable from the furnace. Instead, other means are provided in connection with such devices for gaining access to the combustion area. This is no problem in large installations where there is room for ports for ash removal and the like. The usual home installation does not have sufficient space for various ports. Moreover, the usual port provided for the addition of fuel to a home furnace is likely to be placed in close proximity to the port provided for removal of ash such that mounting a stoker at one port tends to preclude access to the other port, and vice versa.
In U.S. Pat. No. 2,097,564--Durand, a stoker is provided with casters such that it can be wheeled up to a furnace. The Durand device has an overfeed mechanism in the form of a piston, pushing coal horizontally into a chute or trough. The chute extends right over the combustion area, terminating in a closed end whereby as the chute becomes full, pieces of fuel fall from the sides and end of the chute onto the fire below. Of course, placing a chute directly in the combustion area interferes with the flow of air. Furthermore, the chute itself is thereby heated and fuel in the chute will coke and may burn. A quantity of energy is also lost by useless conduction of heat into the stoker.
A similar device to that of Durand is shown in U.S. Pat. No. 1,694,290--St. Clair. In that patent, a caster-carried coal stoker has a tray extending into the fire chamber, the tray holding the coal at all times during combustion. When the bin is emptied, the entire mechanism, including the fuel-support means, is removed from the furnace. Both the Durand and St. Clair devices are hybrids wherein a central part of the combustion supporting structure is intimately associated with the stoker. These devices may be efficient, but they are not suitable for adapting home furnaces, which are already provided with certain attributes (e.g., dimensions and fuel support structures) that are not readily changed in the manner of Durand and St. Clair. Moreover, devices which depend on means constantly exposed to the heat of the furnace are not long-lived.
In order to provide a mechanism that will place a charge of solid fuel, especially soft coal, onto a combustion area, yet not block upward air flow in the combustion area or deteriorate rapidly in the heat and corrosive gases, the invention is adapted to throw the fuel onto the combustion area from the side. Prior art devices such as namely St. Clair and Durand, have been adapted to spill fuel onto the combustion area from a chute located over the combustion area. The other cited patents have likewise relied upon slow reciprocating elements substantially positioned in the combustion area or underfeed techniques that advance the fuel incrementally.
The present invention takes a new and more effective approach in that a means of stoking accomplishes throwing of coal from a device located entirely outside the combustion area of furnace, at the usual fuel-access port. The invention works well for sticky soft coal because the fuel is kept outside the combustion area, and thereby relatively cool (i.e., not subject to coking), until it is actually thrown onto the fire. The invention can also can be used for hard coal. A fuel poker bar intermittently run into the fire agitates the burning fuel synchronously with the drive mechanism, ensuring ready access of air to the coals. The invention does not depend upon any high powered means such as a steam blast for causing a sudden motion necessary for throwing, but instead includes a timer that intermittently activates a motor to rotate a cam shaped wind up and release a spring. Stored energy in the spring is released through a piston to fling the coal. The feed can accordingly be executed in readily-available parts, and applied as a retrofit to coal furnaces of virtually any manufacture.